One of the currently active fields of pharmaceutical research is the inhibition of 5.alpha.-reductase, the enzyme which converts testosterone to dihydrotestosterone, a more potent androgen. It has been demonstrated that inhibitors of 5.alpha.-reductase can block the formation of dihydrotestosterone and ameliorate a number of highly undesirable conditions, including male pattern baldness and benign prostatic hypertrophy. Finasteride, a 5.alpha.-reductase inhibitor is now approved in the United States for the treatment of benign prostatic hyperplasia. Mocellini et al., The Prostate, 22, 291-99 (1993).
Audia et al., have disclosed a series of octahydrobenzo[f] quinolinones which are 5.alpha.-reductase inhibitors. See U.S. Patent 5,239,075; Tet. Let. 44, 7001 (1993) and J. Med. Chem. 36, 421 (1993). The present invention provides an improved process for the synthesis of certain of those compounds.